1. Field of the Invention
The present invention relates to an insulating resin film used for joining an electronic part and a substrate, a bonded structure using the insulating resin film, and a production method of the bonded structure.
2. Description of the Related Art
As one of methods for bonding an electronic part (e.g., an IC chip), and a substrate (e.g., a glass epoxy substrate (PCB)) together, flip chip bonding technology has been known. In the flip chip bonding technology, bumps of the IC chip are arranged to face wirings of the PCB, and the bumps and wirings are electrically connected by bringing the bumps and wirings into contact with each other directly, or via conductive particles, as well as heating and pressing. For the connection via the conductive particles, an anisotropic conductive film (ACF) is used. As the ACF, a film having an epoxy resin-based insulating adhesive layer in which conductive particles are dispersed is generally used. For example, if the ACF is provided between the IC chip and the substrate, and heat and pressure is applied thereto, the conductive particles are sandwiched and crushed by the bumps of the IC chip and the electrode of the substrate, to thereby realize electric connection between the bumps of the IC chip and the electrode.
Recently, along with the trends of downsized and high performance electronic devices, semiconductor devices have been highly integrated. As a result, a space between bumps of an IC chip has been getting narrowed, and an area of each bump has been getting smaller. However, a limit of diameters of the conductive particles to be downsized is approximately 2 μm. As a connection method in a finer region, therefore, a non conductive film (NCF) bonding method has been noted. The NCF bonding is a method where the bumps of the IC chip and the wirings of the substrate are directly bonded via a non conductive film (NCF). In the NCF bonding, stud bumps are used as bumps of the IC chip, and the IC chip and the substrate are directly bonded by crushing the stud bumps with the substrate during pressure bonding of the IC chip and the substrate.
As conventional NCF, a single-layer structure products having high glass transition temperature are in the main stream and those having the glass transition temperature of 150° C. or higher have been used for securing connection reliability. If the IC chip and the substrate are bonded using such NCF by performing heating and compressing, the resultant has excellent connection reliability (connection resistance), however, adherence (die shear strength) between the IC chip and the substrate is poor in a pressure cooker test (PCT).
Conversely, use of the low curing shrinking and highly adhering NCF having the glass transition temperature of lower than 150° C. does not give a degraded adherence in the PCT, but forming voids in the NCF after bonding the IC chip and the substrate because of a slow curing speed thereof.
Contrary to the advantage of the NCF bonding using the stud bumps that it is suited for a fine pitch application, the NCF bonding have problems that the IC chip and the substrate are easily separated from each other because of defects, such as voids formed in the NCF, and floating of bumps.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2001-160568 discloses a bonding material containing thermoset resin, and inorganic filler, and discloses that use of such a material gives excellent reliability after PCT. However, this bonding material is a single material of a single layer structure, and there is no description about whether or not die shear strength is degraded after the PCT.
Moreover, JP-A No. 2000-178511 discloses a method for bonding an IC and a wiring board with an epoxy resin having a laminate structure. In this method, the connection reliability of the bonded structure is improved after aging by giving the epoxy resin a laminate structure, and a difference in melt viscosity. However, it is not disclosed about maintaining die shear strength thereof after the PCT.
Furthermore, JP-A No. 10-289969 discloses a method where a joint ball is used as an electrode of an IC chip, and the IC chip and a substrate are bonded with a two-layer structure NCF. Although the NCF has a two-layer structure in this method, the layer structure is merely formed of a combination of a layer containing inorganic filler and a layer without inorganic filler, the layers using the identical epoxy resin compositions. Therefore, this method cannot prevent formation of voids, or improve adherence between the IC chip and the substrate. Moreover, for the connection between the IC chip and the substrate, joint balls are used. Therefore, no solution for a problem such as floating of bumps, caused in the case where stud bumps are used, is provided.